Conveyor systems are an integral part of modern production facilities. Such systems are especially beneficial in the food processing and article packaging industries, where it is often desirable to move articles to and from different areas of the production facility to undergo various manufacturing/packaging operations. Due to constraints, such as limitations in floor space, it is often necessary to provide bends or curves in the conveyor system to move articles in a desired direction for positioning at a specific location.
A significant problem encountered with present day modular link conveyor belts is concerned with the substantial increase in the drag force in curves as the linear speed of the conveyor increases. Specifically, the inner side links of the belt are compressed upon entering the curve and the outside links are expanded. These competing forces place the conveyor belt in lateral tension along the radius of the curve. This tension, in turn causes the outer links to press against the outer guide rail, which is usually simply a curved, stainless steel channel. It is known that this contact creates the deleterious "hot spots" as the frictional drag force on the conveyor belt escalates. Left unchecked, the frictionally generated heat eventually causes the plastic depending arm of the side link to soften, which can lead to failure.
Even if the speed is reduced sufficiently to avoid failure, the frictional drag force reduces the operating efficiency of the system itself, since more power is required to overcome this force. Even if the heat rise is controlled, the side links of the conveyor belt wear more rapidly, which further increases the incidence of link or belt failure. These difficulties inevitably lead to costly production downtime.
Conventional attempts to reduce the troublesome drag force have met with little success. For instance, it is well-known that providing a constant source of lubrication to the curved guide rails can temporarily reduce friction and the resulting drag force. However, for many production operations, such as food processing, the presence of industrial lubricants presents a significant problem, as the food product is subject to contamination. The lubricants readily trap loose food product and, thus, create an unsanitary residue which provides a breeding ground for bacteria or the like. Furthermore, because of the requirement for frequent washing to meet governmental regulations, even if the lubricant is ruled safe to be around the food product, the cost of frequent reapplication to the rails is prohibitive.
One early proposal for overcoming the above mentioned problems associated with drag force is taught in U.S. Pat. No. 3,094,206 to Stewart. This reference discloses a flexible wire conveyor belt having a pair of centrally-located depending legs with shoulders which track along a series of rollers secured near the center of the conveyor frame. While this proposal seeks to reduce the drag force by substituting rollers for the conventional passive or static guide rail, it is apparent that such a design lacks the stability that is required in modern operations, especially during high speed belt operation. Specifically, the presence of a single guide rail in the center fails to consistently maintain the belt flat, thus leaving the belt edges free to flex upwardly and away from the conveyor support frame.
Modern efforts to improve the tribological characteristics in modular-type conveyors have moved away from the teaching of the '206 patent and have instead sought to alleviate the problem by redesigning the conveyor belt itself. Most, if not all, of such proposals involve the attachment of rollers directly to the underside of the belt to reduce the drag force. During operation, these rollers track along one or more passive guide rails in an attempt to guide the belt along the curve with less friction. For example, U.S. Pat. No. 5,573,105 to Palmaer discloses a modular link conveyor belt having a plurality of rollers carried under the belt. These rollers also engage a center rail. A similar example of such a design is U.S. Pat. No. 5,038,925 to Chrysler, which teaches the use of a conveyor belt having split rollers mounted along its peripheral edge for engaging a passive guide rail.
While these proposals are improvements over conventional approaches, such as the concept of applying a lubrication substance, several limitations still remain. The complexity and expense of the conveyor belt is the main drawback, since the cost of construction more than doubles. Furthermore, with the number of rollers increasing by ten/twenty fold or more, the chances of failure leading to downtime are greatly increased. Also, from a sanitary viewpoint, these extra rollers increase the problem of cleaning the belt to meet the governmental standards.
Still others propose external modifications to the conveyor belt. For example, in U.S. Pat. No. 3,946,857 to Fraioli, Sr., a series of rollers are mounted along the periphery of the conveyor belt for tracking along a passive guide rail. However, it is readily apparent from viewing this proposed design that similar limitations remain; namely, complexity and cost of design, increasing incidence of belt failure, and complicating the cleaning process.
In addition to negotiating curves, it is often beneficial to provide the conveyor belt with up/down ramping capabilities. This added dimension of travel not only provides significant flexibility in moving articles to and from production areas, such as where the work stations have different height requirements, but also where there are different levels of the production facility itself.
Thus, a need exists for a side flexing, modular conveyor system with improved operating characteristics. Such an improved system would be simple in design, inexpensive to construct and maintain, and would include the ability to smoothly and efficiently negotiate horizontal curves or bends by substantially reducing the troublesome drag force associated with passive guide rails. Additionally, the belt would be provided with an improved ability to ramp up and down smoothly and reliably. Further, the improved system and its conveyor belt would lend itself to more efficiently traveling along the return run.